The minimum (or lowest) safe altitude is used in aviation to designate an altitude level deemed safe over a particular flight path such as procedure turns which are part of instrument approaches into airports. Generally, the minimum safe altitude is an altitude level that incorporates a safety buffer above the obstacles and/or terrain within a particular geographic region proximate to a route that an aircraft may travel while executing an instrument approach. The minimum safe altitude is intended to ensure clearance over obstacles and terrain during flight.
Often, the minimum safe altitude is determined based on criteria provided by a governmental or regulatory organization. For example, in the United States, the Federal Aviation Administration defines criteria for the minimum safe altitude in the Federal Aviation Regulations. The regulations may provide a specific safety buffer for determining the minimum safe altitude for a procedure turn, for example, an altitude of 1,000 feet above the highest obstacle within a horizontal distance of four nautical miles. By flying an aircraft at or above the minimum safe altitude, the pilot complies with the terrain and obstacle clearance requirements for the particular procedure turn.
A great many instrument approach procedures require a procedure turn (course reversal) to place the aircraft in a straight in position and direction for the published final approach course. While executing the course reversal or procedure turn, the aircraft is required to remain within a stated distance, typically 10 nm, of some navigational fix on the approach procedure while maintaining a minimum altitude for the reversal turn.
For accomplishing a procedure turn in accordance with instrument flight rules (IFR), the minimum safe altitudes and maximum safe distance are often published on aeronautical charts for the procedure turn for an associated navigation reference point. These aeronautical charts are published as printed procedures or charts, also known as approach plates.
The protected area boundaries are established for a number of reasons such as obstacle clearance, noise abatement or both. This requirement keeps the aircraft in a geographical area that has been inspected and is known to contain no obstacles or terrain that would be a threat to the aircraft, provided that the aircraft is higher than the published minimum altitude and stays within the published mileage of the stated navigational fix published as part of the procedure.
It is up to the pilot to use current navigation aids (GPS, DME) to establish whether the aircraft is within the protected area. This usually requires that the pilot monitor the aircraft navigation position and distance from the fix establishing the mileage limit for the procedure turn. Depending on the navigation source (DME or GPS) and the fix from which the mileage limit was established, the task of flying the procedure turn can become a fairly complex and high workload task. The pilot, for instance, may have to monitor a different page on the GPS unit or a second VOR/DME may have to be tuned to establish the proper distance from the navigation fix and to ascertain whether the aircraft is within the protected airspace. This additional workload is taxing to the pilot while attending to many tasks on the approach.
Generally, a pilot must maintain copies of these printed charts and utilize the proper chart during flight. After identifying the proper chart, the pilot must locate the appropriate procedure turn that corresponds to the intended flight path of the aircraft, the corresponding minimum safe altitude and maximum distance for the procedure turn, and then compare it to the current altitude and distance of the aircraft to determine if the minimum safe altitude and maximum safe distance criteria for the procedure turn is met. The published charts are oriented north-up and often require a pilot to manually rotate and position the chart to orient it based on the current heading of the aircraft. Additionally, these charts often include a variety of other information relating to the given navigational facility, further obfuscating the desired minimum safe altitude and maximum safe distance information. Thus, using and maintaining the printed charts is both cumbersome and confusing.
Accordingly, it is desirable to provide a graphical display of procedure turn airspace, including minimum safe altitude, maximum safe distance from the navigation fix, the current location of the aircraft within the airspace, and an alert when approaching or surpassing the minimum safe altitude and maximum safe distance. Furthermore, other desirable features and characteristics of the exemplary embodiments will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.